Some local interneurones do not spike but communicate with other neurones by the graded release of transmitter, whilst other local interneurones of similar morphology do spike and use the spike to effect intercellular communication. Why should this be? What is it about the particular roles played by these two types of local interneurones in the control of posture and locomotion that requires these different methods of intracellular signalling and intercellular communication? The experimental methods will be multi-disciplinary, combining physiology and morphology to characterize the action of the interneurones and their synaptic relationships. The connections made by the local interneurones and the mechanisms used by them for communication will be revealed by multiple and simultaneous intracellular recordings. Their morphology will be revealed by the intracellular injection of dyes followed by the tracing of their branches into known areas of neuropile. The questions are to be tackled in the central nervous system of the locust because it offers a unique opportunity to make intracellular recordings from interconnected pairs of identified local interneurones in an alert animal and to relate their action to behaviour. This approach will have two outcomes: first, to provide an understanding of the role in behaviour of the two types of local interneurone in one nervous system, and secondly, to resolve the fundamental question of why neurones without axons spike. This is an essential prerequisite for understanding similar local interneurones and similar processes within the mammalian brain.